Synthesis of LiCoO2 cathodes by an oxidation reaction in solution and their electrochemical properties

Layered LiCoO2 was synthesized by an oxidation of Co2+ ions in aqueous solutions by lithium peroxide in the presence of excess lithium hydroxide, followed by firing at 400-900 degrees C. The samples were characterized by X-ray diffraction (XRD) and wet-chemical analysis. Although single phase Li1+xCo1-xO2 samples with a Li/Co ratio > 1 could be obtained at lower firing temperatures, they were metastable and transformed to the stoichiometric LiCoO2 with a Li/Co ratio of 1.0 at higher firing temperatures (T approximate to 900 degrees C). The samples fired at low temperatures (T less than or equal to 700 degrees C) exhibited lower capacity and poor electrochemical cyclability in the lithium cells, due to a disordering of the Li+ and Co3+ ions, and poor crystallinity. On the other hand, the samples fired at 900 degrees C exhibited a capacity as high as 150 mAh/g in the voltage range 4.3-3.3 V, with excellent cyclability due to good cation ordering and crystallinity. (C) 1999 Elsevier Science Ltd.